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The present invention relates to a vehicular headlamp which produces a low-beam light distribution pattern having a horizontal cut-off line and an oblique cut-off line.
As a low-beam light distribution pattern for a vehicular headlamp, as shown in FIG. 10, a light distribution pattern P (L) having a horizontal cut-off line CL1 and an oblique cut-off line CL2 has been employed in many cases. In the low-beam light distribution pattern P (L), the horizontal cut-offline CL1 is arranged to fall on an opposite (oncoming) lane side and the oblique cut-off line CL2, which extends obliquely upward from the horizontal cut-off line CL1, is arranged to fall in the lane in which the vehicle is traveling so as to assure front visibility for the driver of the vehicle while preventing glare for the drivers of oncoming vehicles.
In order to obtain the desired low-beam light distribution pattern P (L), a conventional vehicular headlamp is configured such that a light source 2 is provided substantially coaxially with a lamp optical axis Ax extending in the longitudinal direction of the vehicle, and light from the light source 2 is directed to strike the reflecting surface 4a of a reflector 4 so as to form the cut-off lines CL1, CL2 from light which is reflected from reflecting zones 4a1, 4a2 that are on right and left sides, respectively, of the lamp optical axis Ax.
In the low-beam light distribution pattern P (L), a hot zone (area of high-intensity light) HZ is formed in an area in the vicinity of the left side of an elbow point E (an intersecting point of the cut-off line CL1 and the cut-off line CL2) thereof. The hot zone HZ is mainly formed by light reflected from an area close to the periphery of the reflecting zone 4a2.
A zone D shown by dashed lines in FIG. 10 is a zone where light does not strike the reflector due to the light blocking action of an inner shade 6 positioned directly below the light source 2. Also, a light distribution pattern Po (L) shown by a chain double-dashed line in FIG. 10 is a basic light distribution pattern which occurs if the reflecting surface 4a is constituted by a paraboloid of revolution whose central axis is the lamp optical axis Ax.
However, in the conventional vehicular headlamp, as shown in FIG. 11, if the height of the reflector 4 is reduced, the following problem arises.
The horizontal cut-off line CL1 is formed as a reverse image of a horizontal cut-off line L1 of the lower end edge of the reflecting zone 4a1, and the oblique cut-off line CL2 is formed as a reverse image of an oblique line L2 of the lower end edge of the reflecting zone 4a2. If the height of the reflector 4 is reduced beyond a certain amount, the oblique line L2 falls below the lower end edge of the reflecting surface 4a. 
Accordingly, there arises a problem that the amount of light in the hot zone HZ becomes insufficient, and distant visibility in the traveling lane cannot be sufficiently assured.
The present invention was made in consideration of these circumstances. It is an object of the present invention to provide a vehicular headlamp which produces a low-beam light distribution pattern having a horizontal cut-off line and an oblique cut-off-line, and which enhances the distant visibility in the traveling lane by assuring a sufficient amount of light in the hot zone even when the height of the reflector is small.
The present invention achieves this object by the design of the reflecting surface of the reflector.
More specifically, a vehicular headlamp according to the present invention includes a light source positioned coaxially with a lamp optical axis extending in the longitudinal direction of the vehicle on which the headlamp is mounted, and a reflector having a reflecting surface that reflects light from the light source forward and which provides a low-beam light distribution pattern having a horizontal cut-off line and an oblique cut-off line. In accordance with the invention, the reflecting surface has first reflecting zones which reflect light so as to form the horizontal cut-off line, and second reflecting zones which reflect light so as to form the oblique cut-off line. The second reflecting zones are provided at two positions on right and left sides of the lamp optical axis, arranged diagonally with respect to the lamp optical axis, and the first reflecting zones are provided at two positions on right and left sides which are closer to the periphery of the reflector than the second reflecting zones.
The light source, which is configured as part of a light source bulb, is not limited as long as the light source is mounted substantially coaxially with the lamp optical axis. For example, a filament such as that of a halogen bulb, a discharge light source of a discharge bulb, or the like can be employed. The light source bulb in some embodiments may include light blocking means, for example, an inner shade, a light blocking film or the like, for blocking part of the light directed from the light source to the reflecting surface of the reflector.
The second reflecting zones are not limited in size, outline, shape or the like as long as the second reflecting zones are provided at two positions on right and left sides of the lamp optical axis which are diagonally positioned with respect to the lamp optical axis.
The first reflecting zones are also not limited in size, outline, shape or the like as long as the first reflecting zones are provided at two positions on right and left sides which are closer to the periphery of the reflector than the second reflecting zones.
As described above, the vehicular headlamp according to the present invention provides a low-beam light distribution pattern having a horizontal cut-off line and an oblique cut-off line. The reflecting surface of the reflector has first reflecting zones which reflect light so as to form a horizontal cut-off line, and second reflecting zones which reflect light so as to form an oblique cut-off line. The second reflecting zones are provided at two positions on right and left sides of the lamp optical axis which are arranged diagonally with respect to the lamp optical axis, and the first reflecting zones are provided at two positions on right and left sides which are closer to the periphery of the reflector than the second reflecting zones. With this headlamp, the following actions and effects are obtained.
Since the second reflecting zones are provided at two positions on right and left sides of the lamp optical axis which are arranged diagonally with respect to the lamp optical axis, the amount of light in the hot zone is increased by superimposing the light distribution patterns which are formed by the light reflected from these two second reflecting zones at the two positions.
Therefore, even if the height of the reflector is small and the oblique line which is formed as a reverse image of the oblique cut-off line falls below the lower end edge of the reflecting surface, the amount of light in the hot zone is nevertheless sufficient.
Also, since the first reflecting zone is provided at two positions on right and left sides which are closer to the periphery of the headlamp than the second reflecting zones, even with the second reflecting zones provided at two positions on right and left sides of the lamp optical axis which are arranged diagonally with respect to the lamp optical axis, the desired horizontal cut-off line can be formed.
According to the inventive vehicular headlamp which provides a low-beam light distribution pattern having a horizontal cut-off line and an oblique cut-off line, even if the height of the reflector is small, distant visibility in the traveling lane is enhanced by assuring a sufficient amount of light in the hot zone in the low-beam light distribution pattern. Also, in a vehicular headlamp in which a reflector has a relatively large height, distant visibility in the traveling lane is further enhanced due to the increased amount of light in the hot zone.
In the above-described headlamp configuration, a light source bulb acting as the light source for the lamp may be configured such that part of the light directed from the light source to the reflecting surface of the reflector is blocked by an inner shade. For this purpose, a halogen bulb of the H4 type can be employed. However, if the light source bulb is configured to allow light from the light source to strike the entire zone of the reflecting surface, such as when a halogen bulb of the H7 type is employed, the low-beam light distribution pattern can be formed with a higher luminous intensity by effectively using the entire reflecting surface.